replacement for Volvo 120S saildrive - Help

[Vic]

On our 41 footer we have installed Volvo MD22L engine with 120s saildrive.
Last year the boat sailed for some 4 months and after taking it out of the water the saildrive including the anodes did not show any significant deterioration.
This year after some 4 months sailing the propeller has been lost .
Hence in total the saildrive (brand new engine installation in the boat) has been immersed in sea water for 8 months.
The examination after taking the boat from the water revealed that the saildrive corroded to the extent requiring putting an entirely new one. The loss of the propeller was most likely due to excessive corrosion of the whole assembly.
The reasons for the corrosion are not clear, as the boat is equipped with the galvanically separated shore power.

Now what has frustrated us is the quote from Volvo Polish dealer for the new saildrive. This is almost equal to the price of the complete new set (i.e. the engine with the saildrive). They say this is Volvo's commercial policy not to sell saildrives alone.
We are investigating with the other dealers.
However if it will appear true than we would like to ask, has any one got the experience with fixing another manufacturer's saildrive to a/m Volvo engine ?
In the above circumstances this could be a justified approach.

Kind regards,




<hr width=100% size=1>Victor

 

[steve_cronin]

This IS serious...

We have the same setup and I for one would like to follow your progress on this one. To think that this has happened in such a short time is frightening. Was the galvanic isolator a recent addition or might one of the diodes have failed?

Surely it is going to be cheaper to fit a new drive on labour costs alone? Have you enquired in the UK?

Builders fit these easyfit propulsion units and then leave owners to pick up the costs later down the track.

Steve Cronin

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[Vic]

Re: This IS serious...

I have enquired at Volspec. They are very cooperative but it seems that they are unable to propose anything cheaper (their price is some 4000 pounds, and consider this is the same drive as used by any other MD series engine).
They have suggested to investigate changing only the underwater part of the SD which will be much cheaper, however still some 16 hundred pounds.
We are checking if this is enough.

Still with such prices for spares I would next time consider twice before the purchase of Volvo engine.
I hope that maybe someone on the forum would come with the redundant drive proposal.

Obviously we want to sort out the corrosion problem before putting the new drive.
We have got the full flesh separation i.e. not diode facility but the transformer.
We still can't find the reason.


<hr width=100% size=1>Victor

 

[John_Clarke]

The saildrive and gearbox must be electrically isolated from the engine (and the boats' electrical system) so I am uncertain if a galvanic isolator is significant. Have you checked if you have a very high restistance between the engine and the drive?
I understand it is important to clean the contact area between the anode and the drive before you put the boat in the water again and also to clean the anode to expose fresh zinc. I have also heard that non Volvo replica anodes might not stop corrosion.
If your boat is in fresh water I think it needs a magnesium anode; zinc for salt water.

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[Vic]

John,

Thanks for your valuable advice. The issue of the water can be the reason as the boat last year was parked in Gdañsk which is a river estuary and sailing only on Baltic Sea which is not too salty. This year she went to North Sea for couple of weeks.
We have never checked anode type assuming that it's suitable for any water.
Are all s- drives assembled by the manufacturers as isolated ?

Best regards,



<hr width=100% size=1>Victor

 

[John_Clarke]

All I can tell you is what my manual says - "The drive/reverse gear and flywheel cover are electrically isolated from the engine and must never be used as a ground". The accompanying diagram shows this isolation at the joint between the S drive unit and the engine.
I doubt if this is the problem as long as nobody has connected an earth wire to the saildrive.

Nigel Warren's book "Metal Corrosion in Boats" states about anodes - "Magnesium gives a higher driving voltage, which may be useful, but it has a low efficiency in terms of the electricity it can generate per kilogram weight". It sounds as if this might be your problem.

When cleaning the anode, Volvo say it is important to use emery paper, not a wire brush or other steel tools, as these damage the galvanic protection. Warren says "Iron as an impurity is very harmful because it leads to the formation of a heavy adherent film over the anode which of course reduces the current flow". I do not think this is your problem but I thought I would mention it - I only discovered this because of your question which encouraged me to read up about anodes.

Good luck in the future.

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[Ivy]

Have you painted your bottom with a copper based anti fouling, eg Copper Bot?

I bought a Volvo MD2010 with a sail drive and reading the manual it says "Under water hull, anti fouling agent containing Copper Oxide can increase the risk of galvanic corrosion and therefore should never be used." it also says "The paintwork on the drive is part of the drive's anti-corrosion protection and it is therefore important that any paintwork damage is remedied." It goes on to say how to paint the leg, and that you should use Volvo original primer and top coat, before anti fouling with Volvo anti foul.

Mine has been in the water for two seasons now, and is due to be lifted at the end of October. If there is a problem I will post details later, but hopefuly there won't be.

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[Vic]

Thank you for your advice.
We have checked for the isolation and it appears that 22L engine sd is unfortunately not isolated. We are not able to trace whether this is the neglectance of the authorised service personnel or the manufacturer. The obvious electrical connection is within the speed control lever.
We have looked at another MD 2020 engine where the similar element is thoroughly isolated at the gear box assembly.
We think that the other connection is at the shafts coupling.

Kind regards,

<hr width=100% size=1>Victor

 

[Vic]

Hopefully your sd is OK at the end of season.
I still look forward to receiving the results of you observation.
As I have mentioned in my another reply it appeared that the sd was not isolated.
It was probaly the primary reason for the corrosion, however we do not exclude that inapropriate anode has been fitted to it.

Regards,

<hr width=100% size=1>Victor

 

[steve_cronin]

This worries me a little. How can the drive be isolated from the engine since the driveshaft is metal as is the flange on the drive unit. Also since morse controls connect to both the engine AND the drive, where is the insulation within the control head?

Steve Cronin

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[30boat]

I once rebuilt a friend's volvo 2002 and if memory serves me well the shaft shock absorber had a splined ring ,where the gearbox shaft went, and it was rubber bonded to a disk bolted to the flyweel.This would be enough to insulate the saildrive from the engine.This was a few years back so excuse me if I'm talking nonsense.

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[steve_cronin]

But:-

http://www2.volvo.com/volvopenta/gl...sureboats/saildisplacement/dieselrange/d2-55/ then click on "Product Bulletin"

Shows the engine and gearbox castings very firmly bolted together. However the text actually states that there is a "unique" isolation system between engine and drive. Must be through the engine controls then.

Steve Cronin

<hr width=100% size=1><P ID="edit"><FONT SIZE=-1>Edited by steve_cronin on 03/09/2003 11:35 (server time).</FONT></P>

 

[Vic]

As we have seen on the other model (MD 2020) the cable for the gear control can be properly insulated at the gearbox connection.
The rest of the assembly is probaly insulated by the proper washers, flange etc.
I think that the most critical element is the insulation at the shafts (maybe flywheel) of the engine and gearbox.

<hr width=100% size=1>Victor

 

[oldsaltyfish]

This seems very unusual. My own saildrive has been in salt water for the past 12 years and has no corrosion. I use copper antifoul on the hull and aluminium type antifoul on the leg. The hull also has copper coat on it which is painted over. The half moon anodes last about 2 years and the ring anode three years. I have a bronze prop and have found if I leave it unpainted the anodes will have to be replaced in about a year. If the prop is primed and painted with epoxy the anodes last a lot longer. I usually replace the paint on the prop every three years. I think that you should have a claim under consumer protection laws as the instalation does not seem to meet the intended use of the product. Good luck.

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[Vic]

I think we will follow your both advices as our prop is also bronze and from the discussion it's obvious that there is no doubt on the necessity of the sd insulation.

<hr width=100% size=1>Victor

 

[mikeleslie]

Do you still need a drive? I know someone who was selling a 120s saildrive for 1,000 AUS. It's a 2.4ratio. What ratio are you looking for? It doesn't have a prop, But I have a 15x11 folding 2 blade which I can't use anymore.

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[Gypsy]

Vic, I have a Bavaria 44 with a Volvo D2-55 with saildrive. The saildrive is definately insulated from the engine as tested when the boat was out of the water, including the morse controls, HOWEVER, when in the water the resistance measured between the saildrive and the engine varies according to the location of the boat. At free anchor in the Med the resistance is high (thousands of ohms) but in marinas it could be down to 80ohms or less and this would vary if shore power was connected or not. It is clear that in marinas there are spurious currents in the water for any number of reasons, other boat's hardware, marina electrics/grounding.

After our first year sailing the 3 anodes on the prop and the single one on the leg had deteriorated by more than 50% so we replaced them. The first replacements were Turkish copies of the Volvo parts and when we hauled out for other reasons only 3 months later they were more degraded than the originals after 12mths. I replaced them with Volvo parts so the next test will be when I haul out in 5 weeks time.

The saildrive was painted with the recommended copper-free anti-foul. The bottom of the boat has International Micron Extra.


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[Vic]

Thanks a lot.
Finally we have bought another engine somehow incomplete but with the SD in excellent condition. It was still cheaper than the new SD and we have free spares for the engine.

All the best and kind regards,

<hr width=100% size=1>Victor

 

[Vic]

We have never considered that the anodes might be of such varying quality.
After our extensive investigation I belive that the actual reason for the corrosion was the lack of the proper insulation of the SD at the Morse cables.

Kind regards,

<hr width=100% size=1>Victor

 

[extravert]

I can't help with your problem, but I sympathise with your predicament. When my Bukh saildrive corroded, replacement cost was so expensive that in the end I bought a complete new engine.

I know lots of boaters (and builders) love saildrives, but they soon stop loving them when the leg needs replacing.

<hr width=100% size=1>One day, I want to be a real sailor. In the mean time I'll just keep trying.